Tillage practice greatly influence the temporal variation in magnetic susceptibility in karst depression over the past 60 years

Tillage practices can greatly influence the temporal variation in soil erosion, deposition, and redistribution, and thus soil magnetic susceptibility (MS). In-depth investigation of the distribution characteristics of soil magnetic susceptibility (MS) is helpful to understand the dynamic process of soil redistribution and environmental changes. With the aid of the 137Cs and 210Pbex deposition chronologies, the objective of this study is to investigate the historical changing pattern of MS in a karst depression, and to further evaluate the effects of soil properties, tillage practice, and soil erosion on the temporal variation in soil MS. With collecting representative soil profile samples from cropland and undisturbed bamboo forest land in the karst depression, the MS, soil particle distribution, nutrients, radionuclides and heavy metals were measured. The results showed that mass -specific lowfrequency MS (X-lf) was positively correlated with percentage frequency -dependent MS (Xfd%) (P < 0.001), and the corrected X-fd% was close to the saturation value (11 %) after removing the influence of the initial aeolian signal. The relationship between MS and soil properties is different under cropland and bamboo forest land. For undisturbed forestland, X-lf and X-fd% were both positively related to nutrients concentration (P < 0.001), but negatively related to heavy metal concentrations (P < 0.001). For the cropland with frequent tillage practices, Xlf was positively related to total phosphorus (TP) and heavy metals concentration. Based on the identified MS deposition history, from 1949 to 2015, X-lf and Xfd% showed a significant increase at first and then tended to be stable, and were negatively related to sediment deposition rate (P < 0.001). This study emphasizes the pronounced influence of tillage practices and soil erosion on the temporal variation of soil MS, is helpful for targeted land management strategies in these environmentally vulnerable karst regions.